1. Field of the Invention
The invention relates to gas turbine inlet guide vane ice detection and control systems and methods. More particularly the invention utilizes active infra-red monitoring of inlet guide vanes, detection of ice formation on the guide vanes and elimination of the ice by altering properties of the gas turbine inlet intake airflow, such as by introducing compressed and/or heated air bled from the turbine.
2. Description of the Prior Art
Gas turbines risk ice formation on inlet guide vanes and subsequent ice ingestion when relative humidity and temperature properties of engine intake air within the turbine inlet drop its dew point below water freezing temperature. Intake air flows at sufficiently high velocity to lower its temperature below that of ambient air. Therefore, while ambient air temperature may be above the water freezing point, the combination of relative humidity and lower air temperature within the turbine intake may lead to ice formation on inlet guide vanes. When ice breaks off an inlet guide vane it is ingested by the turbine, potentially causing damage to internal components such as blades and vanes.
In order to reduce risk of ice formation turbine operators monitor intake air properties, such as humidity and temperature, and alter those properties to maintain the dew point above water freezing temperature as an indirect empirical way to prevent ice formation. Relatively conservative turbine operating procedures are followed, based on empirical rules. For example, specific quantities of compressed air can be bled from the turbine compressor section and introduced within the intake airflow to lower relative humidity and raise the dew point temperature when monitored air properties based on rigid control settings or reference to temperature-humidity charts supplied by turbine manufacturers. Heated air bled from the combustor section may be introduced into the airflow to raise its temperature so that any condensed moisture is above water freezing temperature. In some operating circumstances both compressed and heated air may need to be introduced into the air intake airflow. It is desirable to minimize compressed or heated air bleeding as they lower gas turbine operating efficiency. The bled air otherwise would be used to generate additional power in the gas turbine. Empirical rule-based air bleed operational procedures often intentionally factor additional higher safety margins to minimize potential ice formation and ingestion variables that cannot be totally foreseen under all operating conditions. The added conservative safety margins further reduce turbine operating efficiency.
Thus, a need exists for a gas turbine inlet guide vane ice formation monitoring and control system that reduces quantity and/or frequency of compressed and/or heated air bleed from the gas turbine in order to improve operating efficiency.
Another need exists for a gas turbine inlet guide vane ice formation monitoring and control system that directly monitors ice formation and takes corrective action to modify intake airflow properties by introducing bleed compressed and/or heated air based at least in part on the observed need to stop observed ice formation conditions.